Spin Transport in $\hbox {Co/Al}_{2}\hbox {O}_{3}/\hbox {Alq}_{3}/\hbox {Co}$ Organic Spin Valve

Organic spin valve devices with Co/Al₂O₃/8-hydroxyquinoline-aluminum (Alq₃)/Co sandwich structure were fabricated and studied. Spin transport properties in the devices were investigated by measuring the current-voltage behavior and magnetoresistance (MR) at low temperature. With Al₂O₃ insertion, the relatively larger and positive MR ratio was observed with maximum value of around 19% at 5 K. The MR ratio was reduced with increasing temperature and finally disappeared above 80 K. In the case of devices without Al₂O₃ inserted layer, we have not observed MR at measured temperature. The role of Al₂O₃ inserted layer, spin transport mechanism, and the decrease of MR with increasing temperature in the organic spin valve were discussed.